1. Field of the Invention
The invention relates to a diesel filter provided in a fuel supply system of a vehicle and the like, particularly to a diesel filter that improves water separation performance and/or reduces maintenance costs.
2. Description of the Related Art
Diesel engines have long been used as engines for vehicles and the like. In a diesel engine, a filter filters light oil in a fuel tank, and an injection pump compresses the filtered fuel to a high pressure, and an injector injects the fuel to a combustion chamber of the engine, whereby self-combustion takes place in the combustion chamber.
Incidentally, fuel includes foreign matters, for example, water, dust, and solid undesirable materials such as rust. These foreign matters need to be removed because inclusion thereof results in reduced combustion efficiency and wear of the injector or the like. Diesel filters are, therefore, provided to deal with such problems. More specifically, water content in fuel is classified into dissolved water and free water. Dissolved water causes no negative effects, because it flows smoothly in fuel channels and is consumed together with fuel. Meanwhile, free water may cause some problems as follows. Free water appears in fuel when: rainwater intrudes into the fuel during fueling; water droplets formed by moisture in the air intrude into the fuel; or the water dissolved in the fuel is separated therefrom due to a decrease in fuel temperature. Such free water is large in specific gravity compared to light oil, so that it stagnates in the injection pump and the like, thus generating rust and stick. For this reason, free water particularly needs to be removed using a diesel filter.
Auto parts are required to be easily disassembled taking consideration of cost reduction and environmental conservation. Diesel filters for automobile use are desired to have such structure.
A diesel filter related to the invention will be described. A diesel filter includes a cup-shaped case forming an outer shell, and a cap detachably attached to an upper opening end of the case. The cap is provided with a fuel supply pipe, a fuel discharge pipe, and a hand pump. The supply and discharge of fuel are performed through the fuel supply pipe and the fuel discharge pipe respectively, and air is released from the fuel supply system by means of the hand pump.
Housed in the case is a filter member that includes an element having a fuel passage at the center thereof, and an upper holding member and a lower holding member for holding the upper and lower ends of the element. A water reservoir is formed below the filter member.
Fuel is introduced to the water reservoir through the fuel supply pipe and the fuel passage. The introduced fuel changes its direction by 180° in the water reservoir, and then moves upward. Then, the fuel is filtered by passing through the element and discharged from the fuel discharge pipe. When the flow direction of the fuel changes in the water reservoir, water is separated from the fuel. The separated water has a larger specific gravity than the fuel, so that the water is retained in the water reservoir (see Japanese Patent Application Publication No. JP-A-2003-172224).
Note that the amount of water retained in the water reservoir becomes larger as the flow rate of fuel passing through the element reduces. The experiment using the related art device described above shows that the amount of water retained in the water reservoir is not large when the flow rate of fuel is high, as indicated by, for example, the curve denoted by “CENTER FLOW” in the diagram of FIG. 11. Conceivably, this is because all the fuel flows into the water reservoir through the fuel passage arranged at the center of the element, so that the fuel flowing into the water reservoir strongly strikes the center of the bottom thereof, whereby the free water is pushed up to the bottom of the element, and a portion thereof is discharged from the fuel discharge pipe together with the fuel. Thus, it has been proved that desired water retainability can not be always achieved in the water reservoir of the related art device.
In this related art device, in addition to a sealed position between the case and the cap, two other sealed positions are required between the filtering portion and another member. Thus, additional man-hours and further accuracy are required for assembly work.
Moreover, when the filter member is held by the case and the cap, the filtering portion is held by utilizing the upper and lower surfaces of the filter member. Accordingly, an upper holding member and a lower holding member are essential. Thus, the number of parts of the filter member is increased for these two members. This also leads to a problem that disassembly work becomes complicated at the time of disposal.
A diesel filter, as another related art, includes a cup-shaped case forming an outer shell, and a cap detachably attached to an upper opening end of the case. The cap is provided with a fuel supply pipe, a fuel discharge pipe, and a hand pump. The supply and discharge of fuel are performed through the fuel supply pipe and the fuel discharge pipe respectively, and air is released from the fuel supply system by means of the hand pump.
Housed in the case is a filter member that includes an element and a holding member for holding an upper end of the element. Formed below the filter member is a water reservoir. The holding member includes a first member that constitutes a lower portion thereof and holds the element, a second member arranged above the first member with a space therebetween, and a third member provided on the second member. An inlet port is so provided as to pass through the center of the second member and the third member, while an outlet port is so provided as to pass through the first member to the third member. The case, the element, and the holding member including the first member to the third member are assembled into a single unit by caulking to form a cartridge case. Then, a diesel filter is assembled by fixing the cartridge case to the cap.
Fuel is introduced to the space, from the upper center thereof, between the first member and the second member through the fuel supply pipe and the inlet port. The fuel is then introduced to the water reservoir through a fuel channel formed between an inner peripheral surface of the case and an outer peripheral surface of the element. The introduced fuel changes its direction by 180° in the water reservoir, and moves upward. Then, the fuel is filtered by passing through the element and discharged from a fuel discharge pipe through the outlet port. When the flow direction of the fuel is changed in the water reservoir, water is separated. The separated water has a larger specific gravity than the fuel, so that the water is retained in the water reservoir (see Japanese Patent Application Publication No. JP-A-8-291776).
In this related art device, the degree of water atomization is lower than the related art device firstly described, and therefore the amount of water passing through the element reduces. However, its structure is more complicated and the number of parts is larger than the device firstly described. Further, the unit is assembled by caulking the components, which complicates its disassembly. Accordingly, the related art device is not desirable in terms of environmental friendliness.